1. Field of the Invention
The present invention relates to a transistor that uses an oxide semiconductor layer, a semiconductor device including the transistor, and a manufacturing method of the transistor and the semiconductor device.
2. Description of the Related Art
There are various kinds of metal oxides, which are used for a wide range of applications. Indium oxide is a well-known material and used as a material of a transparent electrode which is needed in a liquid crystal display or the like.
Some metal oxides exhibit semiconductor characteristics. In general, metal oxides serve as insulators; however, it is known that metal oxides can serve as semiconductors depending on the combination of elements included in the metal oxides.
For example, tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like can be given as metal oxides exhibiting semiconductor characteristics, and thin film transistors in which a channel formation region is formed using such the metal oxides are already known (Patent Documents 1 to 4, Non-Patent Document 1).
As the metal oxides, not only single-component oxides but also multi-component oxides are known. For example, InGaO3(ZnO)m (m: natural number) having a homologous series is known as a multi-component oxide semiconductor including In, Ga, and Zn (Non-Patent Documents 2 to 4).
Further, it is proved that an oxide semiconductor formed using an In—Ga—Zn based oxide as described above can be used for a channel layer of a thin film transistor (also referred to as a TFT) (Patent Document 5, Non-Patent Documents 5 and 6).
However, semiconductor characteristics are likely to vary because of damage to the oxide semiconductor due to an etchant or plasma or contamination of an element such as hydrogen to the oxide semiconductor in an element manufacturing process. Accordingly, problems of variation and deterioration in electrical characteristics of the element are caused.
[Reference]
[Patent Document]
    [Patent Document 1] Japanese Published Patent Application No. S60-198861    [Patent Document 2] Japanese Published Patent Application No. H8-264794    [Patent Document 3] Japanese Translation of PCT International Application No. H11-505377    [Patent Document 4] Japanese Published Patent Application No. 2000-150900    [Patent Document 5] Japanese Published Patent Application No. 2004-103957[Non-Patent Document]    [Non-Patent Document 1] M. W. Prins, K. O. Grosse-Holz, G. Muller, J. F. M. Cillessen, J. B. Giesbers, R. P. Weening, and R. M. Wolf, “A ferroelectric transparent thin-film transistor” Appl. Phys. Lett., 17 Jun. 1996, Vol. 68 p. 3650-3652    [Non-Patent Document 2] M. Nakamura, N. Kimizuka, and T. Mohri, “The Phase Relations in the In2O3—Ga2ZnO4—ZnO System at 1350° C.”, J. Solid State Chem., 1991, Vol. 93, p. 298-315    [Non-Patent Document 3] N. Kimizuka, M. Isobe, and M. Nakamura, “Syntheses and Single-Crystal Data of Homologous Compounds, In2O3(ZnO)m (m=3, 4, and 5), InGaO3(ZnO)3, and Ga2O3(ZnO)m (m=7, 8, 9, and 16) in the In2O3—ZnGa2O4—ZnO System”, J. Solid State Chem., 1995, Vol. 116, p. 170-178    [Non-Patent Document 4] M. Nakamura, N. Kimizuka, T. Mohri, and M. Isobe, “Syntheses and crystal structures of new homologous compound, indium iron zinc oxides (InFeO3(ZnO)m (m: natural number) and related compounds”, KOTAI BUTSURI (SOLID STATE PHYSICS), 1993, Vol. 28, No. 5, p. 317-327    [Non-Patent Document 5] K. Nomura, H. Ohta, K. Ueda, T. Kamiya, M. Hirano, and H. Hosono, “Thin-film transistor fabricated in single-crystalline transparent oxide semiconductor”, SCIENCE, 2003, Vol. 300, p. 1269-1272    [Non-Patent Document 6] K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, “Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors”, NATURE, 2004, Vol. 432, p. 488-492